Abstract
A technique that provides a first approximation to the mean σ 0 and gradient σ 1 components of residual stress in a thin film material is discussed. In the method, measurements are made on a single micromachined cantilever, as opposed to an array of structures as is used in the related critical-length buckling approach, and tensile, compressive, and gradient stresses are found. The measured deflection profile of a cantilever is broken down into rotation and curvature components, which are shown to derive essentially independently from σ 0 and σ 1 , respectively. Key to the method is the observation that a micromachined structure with a nominally `clamped' boundary undergoes subtle rotation at its junction with the portion of the thin film that remains bonded to the substrate but is contiguous with the structure. This boundary rotation effect occurs through in-plane expansion or contraction of the bonded film following relief of residual stress. Thus, the deformation of the micromachined cantilevers considered here, and of more general bulk- or surface-micromachined devices, can be strongly influenced by the state of stress in the still-bonded film.